1. Centre Block:

Centre block is the basic building block of a universal joint. It provides support to the forks used in the joint. It consists of two hollow cylinders joined together at right angles to each other. Holes in the centre block are meant to accommodate pins. You can understand a centre block clearly by taking a look at the image shown below:

Note: Depending on the type of universal joint, the shape of the centre block may vary. In the universal joint used in automobile propeller shafts, the hollow cylinders of the centre block would be lined up. It is called cross piece.

2. Fork:

Two Forks are used for providing support to the shafts that are to be connected using the universal joint.

A typical fork consists of a central hole to support shaft and a keyway to accommodate shaft key. It also contains two holes to support a pin. Forks are designed in such a manner that they fit accurately over the centre block. You can understand the structure of a fork by taking a look at the following image.

3. Pin:

It is a component used for securing the fork to the centre block. It contains a tapered hole to accommodate a taper pin. In a universal joint, two pins are used to connect two forks to the centre block. The following image illustrates a pin: